The gift of the Holy Spirit has a now/not yet aspect, as is seen in three New Testament metaphors:-

1.  Commercial.  The Holy Spirit is like the down-payment in a purchase.  He is both the first instalment and the guarantee that the full payment will follow.  2 Cor 1:22; Eph 1:14.

2.  Agricultural.  The gift of the Sprit is like the harvesting of the first-fruits.  It is both the beginning of the harvest and the gurantee that the rest will follow.  Rom 8:23.

3.  Social.  The gift of the Spirit is like the first course of a banquet.  It is both the foretaste and the guarantee of the meal that will follow.  Heb 6:4f.

See Stott, Evangelical Truth, 128f.